For example, the X-ray imaging device can comprise a six axis articulated aim robot which, downstream of a plurality of arms, has a hand which carries the X-ray source and the X-ray detector, said X-ray source and X-ray detector each being movable separately relative to the hand.
A 3D reconstruction is a method for obtaining a 3D image dataset in which grayscale values are assigned to volume elements of the three-dimensional space occupied (at least partly) by the object of interest. The grayscale values indicate the degree of attenuation of the X-radiation by the object of interest in the region of the respective volume element.
To obtain a 3D-image dataset using a 3D reconstruction, a sequence of two-dimensional X-ray images is taken. These are also known as projections because the object of interest is projected onto the plane of the X-ray detector using an X-ray source assumed to be virtually a point source. For example, by means of what is known as the (filtered) back projection process, contributions to the grayscale values can then be calculated for the volume elements. For back projection it is necessary to know the mapping rule from the X-ray source onto the X-ray detector. The mapping rule is usually specified as a so-called projection matrix.
X-ray imaging devices of simple construction have only a few degrees of freedom as regards the movement of the X-ray source and X-ray detector. The parameters for these degrees of freedom are run through systematically and image recordings of a calibrating object, known as a calibrating phantom, are made at a plurality of positions. For a known appearance and known location of the calibrating phantom, the projection matrix can be calculated for a respective position on the basis of these image recordings.
More modern X-ray imaging devices, such as those with a six axis articulated arm robot, have such a large number of degrees of freedom that it is no longer possible to run systematically through every combination of parameters of the individual components. This problem is overcome using interpolation or extrapolation in respect of the projection parameters in the projection matrices. However, the results thus obtained are unsatisfactory, the 3D reconstructions being of a less than desirable quality.